[a/s] Old Furnaces- warning- long and boring

[Chris Bryant <bryantrv@xxxxxxxxxx>]

Hi Gang,
	Rich was right on the money in his explanantion of the old Suburban
furnaces, but I thought I would try to add some things. (Warning- long and
boring to follow..)

	The three biggest problems with these old furnaces are rust, rust, and
rust...

	But seriously, they really are not that complicated. The sequence of
operation is (kind of) as follows.
	You light the pilot, while pushing a button that opens a safety valve. The
pilot  is trained on the thermocouple. The thermocouple generates a very
small electrical current that keeps the safety valve open, providing gas to
the main valve.

	When you turn up the thermostat, the fan relay closes, starting the fan
motor, which starts, closing a sail switch. Onse the sial switch closes,
power is supplied to the main gas valve, opening it, providing gas to the
main burner.

	When the furnace gets hot enough, a thermal fan switch closes, that keeps
the fan running even after the thermostat is satisfied, until almost all of
the heat is blown off the heat chamber. (There is also a limit switch in
there that turns the main gas valve off if the furnace gets too hot).

	In the old Suburban furnaces, the main failures are:

	The burner getting clogged by rust (the flame should be "hard" looking and
blue)- solution- remove the burner and clean the slots with a hacksaw blade.

	The pilot orifice getting clogged- solution- you can *try* to clean it by
soaking in alcohol and blowing out with compressed air- but I usually just
replace them- the hole is so small (2 holes actually- each .0035")that they
are very hard to clean. Suburban p/n 160659- around $5-6.

	The whole heat chamber rusting out- the places to look are at the front
bottom of the chambers- solution- new furnace..
	The design of the furnace is such that the air intake and exhaust are
right next to each other on the outside of the trailer- so in a windy
situation, the air pressure will be equal on both ports, and air will not
"whoosh" through the heat chamber.
	When the chamber gets rusty, the air can travel through- blowing out the
pilot.

	The recall was for the "crossover tube", a tube in the rear of the furnace
that takes the combustion air from the intake blower to the burner. The
original was made of inferior materials, and would crack.

	Suburban no longer sells (many) parts for these furnaces, but if the heat
chamber and gas valves are in good shape- they do a very good job.
	The best thing to do is to pull them out and give them a thorough cleaning
and inspection.If anyone is interested, I can e-mail removal instuctions to
you or the list- but I think now I have rambled on too much.. :-)



________
	
	Chris Bryant
	Bryant RV Services
	DeLand, Florida
	mailto:bryantrv@totcon.com